This invention relates to an organohybrid-based damping material, a method for producing the same and a damping improver for the organohybrid-based damping material. More particularly, it relates to the damping material, which efficiently absorbs mechanical energy and dissipates it as thermal energy to dampen unwanted noise and vibration, comprising a polymer matrix and an organic damping improver exhibiting piezoelectric, dielectric and electroconductive effects.
The damping material provided by the present invention is high in damping efficiency, controlled in functional deterioration when put in service for extended periods, and applicable to different application temperature regions and wide areas, including electric appliances, machines, chemistry, construction/civil engineering, and transportation.
Damping of vibration and noise has become an important requirement in the design of automotive and aerospace structure. Active and passive damping are two types of generally used methods for the control of the unwanted vibration and noise. Passive damping control generates more increased interest due to its reduced system complexity. In such a system the damping material, which can convert sound or mechanical vibration energy into heat plays a important role.
One of normal measures against noise produced by, e.g., home electric appliances and vehicles, especially while they are running on highways and bridges, are thick walls of metal and inorganic materials. The damping efficiency of such materials obeys mass law, i.e., increasing their weight will reduce noise more efficiently. However, increasing thickness or weight of sound insulating walls of inorganic materials needs high costs and special structural considerations. Although porous fibers (e.g., rock wool, glass wool and other porous fibers) can be used to decrease the weight of sound and vibration insulating materials, these materials have insufficient damping efficiency in a low frequency region, and can not reduce the size or thickness of insulating wall. On the other hand, double-structured walls for reducing wall weight may result in a decrease in sound transmission loss at a specific frequency because of the resonance produced by the wall masses and air spring between them, causing insufficient sound insulation.
Another of typical candidate materials for the application of passive damping are viscoelastic polymers, which are relatively lighter and exhibits higher damping efficiency compared to metal and inorganic materials. Since the dissipation of the mechanical energy of a polymer is most efficient in the vicinity of its glass transition temperature, a polymer with a higher damping peak around application temperature is preferred. However, the glass transitions of most polymers are distant from room temperature unfortunately. Therefore, either how to control the damping peak position to locate within a required temperature region or to enhance the damping peak intensity of the polymer-based damping material is of great importance. Although the use of interpenetrating polymer networks (IPN) obtained from emulsion polymerization has been thought a very effective way to broaden the damping peak, it is often applied as paint instead of a structure material due to the difficulty of elimination of water. Blending binary or ternary polymers with moderate miscibility has been considered as another approach to damping peak broadening, whereas the location of damping peak position is restricted within the glass transitions of two polymers, and it fails to improve the damping peak intensity. The addition of small-molecular-weight plasticizer indeed causes an increase in the damping peak maximum, but the damping peak position is shifted to a lower temperature and the storage modulus is reduced unfortunately. On the other hand, polymeric composites filled with inorganic particles or fibers can provide high stiffness and strength, whereas the damping peak maximum decreases sharply.
To solve the above-mentioned problems, a polymer-based composite damping material containing piezoelectric ceramic powders and electrical conductive particles has been developed. The damping mechanism of such a composite is assumed to be due to the energy transferring effect through the cooperation among the components. The mechanical vibrating energy is first transmitted to the piezoelectric ceramic powder, and converted into alternating electrical potential energy by the piezoelectric effect. Then, the electrical potential energy is further converted into Joule""s heat through the networks of electrical conductive particles in the polymeric matrix. Although the damping mechanism of such a kind of composite is unique, this damping material exhibits low loss tangent (tan xcex4) of 0.5 or so at the highest due to the dismatch between the inorganic filler particles and polymer matrix, resulting in insufficient damping efficiency for practical use unfortunately. To improve the interaction among the components, a damping material comprising an organic low-molecular-weight additive and a polymer matrix has been also proposed. For example, Japanese Patent Application Laid-Open No. 68190/1999 disclosed a damping material comprising N,N-dicyclohexyl-2-benzothiazolyl-sulfenamide as the organic low-molecular-weight additive and chlorinated polyethylene as the matrix. Those proposed so far, however, have a disadvantage of insufficient stability, deteriorating in the functions when put in service for extended periods due to the phase separation resulting from massive formation of the free crystals, wherein N,N-dicyclohexyl-2-benzothiazolyl-sulfenamide is the main component. Meanwhile, these attempts have failed to control the damping peak position to locate within a required temperature region.
From the viewpoint of application, the best polymer-based damping material should possess both excellent damping and high stiffness, while its glass transition can be controlled to meet different practical requirements. The inventors of the present invention also found that increasing loss tangent (tan xcex4) and loss modulus (Exe2x80x3) simultaneously is required to enhance the efficiency of vibration and sound absorption of the damping material. However, as described above, no material satisfying the above requirements has been developed up to now.
It is an object of the present invention to provide an organohybrid-based damping material, which is composed of a polymer matrix and an organic damping improver exhibiting piezoelectric, dielectric and electroconductive effects. This damping material shows a high degree of damping efficiency and a limited extent of temporal deterioration. Moreover, the damping peak position can be controlled to locate within a required temperature region.
It is another object of the present invention to provide an organic damping improver, which comprises at least one organic piezoelectric, dielectric and electroconductive material containing basic nitrogen and one specific organic additive. The damping improver both enhances damping efficiency excellently and improves the stability of damping properties against aging successfully, and achieves the control of damping peak position to locate within a required temperature region as well.
It is still another object of the present invention to provide a method for producing the organohybrid-based damping material and the damping improver. The manufacturing methods include the selection of the components, the mixing procedure and molding process to obtain the final products.
It is still another object of the present invention to provide a damping material which satisfy both the loss tangent (tan xcex4) and loss elastic modulus (Exe2x80x3) requirements simultaneously. This means that the invented damping material possesses both excellent damping efficiency and high stiffness. The present invention also provide a method for producing the material to achieve the above purposes.
The inventors of the present invention have noticed that for the damping improver, importance of the second specific organic additive, which shows a strong interaction with the organic piezoelectric, dielectric and electroconductive material containing basic nitrogen and can efficiently control the crystallization and crystal growth of the components. The inventors have also found that the second additive has a synergistic effect on the damping improvement with the piezoelectric, dielectric and electroconductive material, and a specific phenolic compound having a suitable molecular weight is useful for the above purposes based on extensive studies.
The first invention relates to an organohybrid-based damping material, comprising a polymer matrix having a polar side chain and an organic damping improver exhibiting piezoelectric, dielectric and electroconductive effects. The damping improver is composed of a mixture of a compound (I) containing basic nitrogen and a phenolic compound (II):
(I) at least one compound containing basic nitrogen, selected from the group consisting of sulfenamides, benzothiazoles, benzotriazoles and guanidines, and
(II) at least one phenolic compound shown by the general formula (1): 
wherein,
(1) R1 and R2 are each a hydrocarbon group having a carbon number of 1 to 10, and may be the same or different,
(2) (n) and (nxe2x80x2) are an integer of 0 to 3, and may be the same or different,
(3) (m) and (mxe2x80x2) are an integer of 1 or 2, and may be the same or different,
(4) (s) and (t) are an integer of 1 to 3, and may be the same or different, and
(5) X is at least one bonding group selected from the group consisting of oxygen atom, sulfur atom, a halogen atom, a hydrocarbon group which may contain at least one of the above atoms and has a carbon number of 1 to 20, and a group containing an ester linkage.
The ratio of the polymer matrix and the damping improver is from 80/20 to 20/80 by weight.
The second invention relates to an organic damping improver, which is to be incorporated in the polymer matrix to exhibit piezoelectric, dielectric and electroconductive effects, and is composed of a mixture of a compound (I) containing basic nitrogen and a specific phenolic compound (II):
(I) at least one compound containing basic nitrogen, selected from the group consisting of sulfenamides, benzothiazoles, and guanidines, and
(II) at least one phenolic compound shown by the general formula (1): 
wherein,
(1) R1 and R2 are each a hydrocarbon group having a carbon number of 1 to 10, and may be the same or different,
(2) (n) and (nxe2x80x2) are an integer of 0 to 3, and may be the same or different,
(3) (m) and (mxe2x80x2) are an integer of 1 or 2, and may be the same or different,
(4) (s) and (t) are an integer of 1 to 3, and may be the same or different, and
(5) X is at least one bonding group selected from the group consisting of oxygen atom, sulfur atom, a halogen atom, a hydrocarbon group which may contain at least one of the above atoms and has a carbon number of 1 to 20, and a group containing an ester linkage.
in a compound (I)/compound (II) ratio of 100/2 to 50 by weight.
The third invention relates to a method for producing the damping material composed of a polymer matrix and an organic damping improver exhibiting piezoelectric, dielectric and electroconductive effects, and comprising the following steps (a) and (b):
Step (a): a step of uniformly mixing (1) the polymer matrix and the material exhibiting piezoelectric, dielectric and electroconductive effects, and (2) the above mixture and the second specific additive which shows a strong interaction with the organic piezoelectric, dielectric and electroconductive material containing basic nitrogen and can efficiently control the crystallization and crystal growth of the components, as well as the fourth constituent material, at room temperature or higher by a two-roll mill, an extruder or other mixers, and
Step (b): a step of molding the mixture produced by the above step (a) at a temperature from 40 to 200xc2x0 C. by hot pressing, stretching, extrusion, injection or other molding processes.